The invention relates to a device for propelling high speed water borne craft. This device permits an efficient machinery arrangement within the craft and precludes the loss of efficiency associated with traditional fully submerged inclined shaft propellers.
Horizontal shaft arrangements have been used to increase the efficiency of the propellers thrust by allowing the propeller blades to be positioned at a right angle to the flow stream. When horizontal shafts were used, machinery arrangements were cumbersome, extra gears had to be used and loss of efficiency due to transverse forces in the gearing system occurred.
When inclined shafts are used, traditional fully submerged propellers were placed at a non-orthogonal and therefore inefficient angle to the flow stream. If a fully submerged raked propeller were used, only a small increase in efficiency would be provided by arranging the rake so that the blade of the propeller were perpendicular to the stream during the downward stroke of each blade, since during the upward stroke of each blade, much of the effectiveness of the propeller would be lost. Only a small portion of that loss of effectiveness is tempered by the fact that the upper portion of the stream would be disturbed by the passing of the strut or vessel itself.